In recent years, the specifications for finished lubricants require oil formulators to develop finished lubricants that contain less phosphorous while also providing reduced mechanical wear and increased lubricant life spans. Moreover, while lubricant performance specifications have been increased, the treat rate for lubricant additives has been decreased. Also required is a reduction in mechanical friction so as to meet energy saving trends.
A wide variety of compounds for use as lubricating oil friction modifiers are known. These include nitrogen containing compounds such as amines, imines and amides, oxygen containing compounds such as fatty acids and full or partial esters thereof, and oil soluble or oil dispersible molybdenum compounds such as dinuclear molybdenum dialkyldithiocarbamates and trinuclear organomolybdenum compounds, to mention but a few.
Often combinations of specific additives are reported to produce synergistic effects, and in some cases, a change in the concentration of the combined additives reverses the overall effect. Additionally, it has been observed that the overall effect of additives depends not only on the nature and concentration of the additives, but on the nature of the oil as well. The invention disclosed herein lends support to the observation that the base oil of a lubricant formulation may have an influence on additive performance, especially a dual additive in a complex mixture.